(a) Technical Field of the Invention
This invention is related to a complex cooling fan and in particular to one which has increased cooling capacity and can be manufactured at a low cost.
(b) Description of the Prior Art
There are two ways to increase the cooling capacity of a cooling fan, i.e. increasing the area of the blade and forming an air passage between two adjacent blades. However; in order to enable the conventional cooling fan to be released from the injection molds, there must be a distance between the vertical projection of the upper point of a blade of a conventional cooling fan between the vertical projection of the lower point of an adjacent blade of the conventional cooling fan thereby making it impossible to form an air passage between two adjacent blades and therefore rendering it difficult to increase its cooling capacity. Hence, it has been proposed to make the vertical projection of the upper point of a blade coincide with the vertical projection of a lower point of an adjacent blade so that the molds must be formed with sharp angles in order to achieve this purpose thus making the molds easily damaged in working and transportation. As shown in FIG. 1, the conventional cooling fan 1 has a body 11 on which there are a plurality of blades 12, wherein the vertical projection of the upper point 12a of a blade is coincide with the vertical projection of the lower point 12b of an adjacent blade. Hence, there will be a first acute angle 14 between the mold releasing line 13 and the upper point 12a and a second acute angle 15 between the mold releasing line 13 and the lower point 12b. Accordingly, there will be a sharp angle A3 between the male mold A1 and the female mold A2 (see FIG. 2), thereby making the molds be easily damaged.
Therefore, it is an object of the present invention to provide an improvement in the structure of a cooling fan which can obviate and mitigate the above-mentioned drawbacks.